Electrical contact device



March 3, 1931. 5 LODGE I 1,795,090

I ELECTRICAL CONTACT DEVICE Filed March 8, 1929 ill Patented Mar. 3, 1931 UNITED STATES PATENT OFFICE EDMUND GEBERT LODGEt-OI' PHILADELPHIA, PENNSYLVANIA, ASSIGNOB TO AT- WATEE KENT MANUFACTURING COMPANY 01 PHILADELPHIA, PENNSYLVANIA,

A GOKPORATION OF PENNSYLVANIA mmcrnrcat comac'r Dawes Application fled larch 8,

My invention relates to volume control rhecstats for radio receiving apparatus, in which noise-producing imperfect contact is prevented by recourse to structure of the character hereinafter described, including a sliding contact member adapted to rock or oscillate about its axis transverse to its direction of travel to maintain it in multipoint contact with a resistance element.

My invention resides in movable contact structure comprising a resilient contact member pivot-ally supported at one end, and in engagement with a yielding abutment adjacent its free or contacting end; more particularly the yielding abutment comprises a resilient supporting member, fixed at one end. the free end of which comprises a fulcrum adapted to enga e and bias the resilient contact arm more firmly into engagement with its cooperating contact; and more particularly the contact and resilient supporting members are mounted coaxially and in superposed relation with respect to each other.

My invent1on further resides in movable contact structure of the character above described wherein the yielding abutment engages the contact member at a point on its longitudinal axis, whereby oscillation of the contact member with respect to its longitudinal axis is permitted; more particularly the cooperating or stationery element with which the movable contact member coacts comprises a curvilinear resistance element, specifically a coiled resistance wire, upon the surface of which rid-es the movable contact with minimum friction; more particularly the resilient supporting member has less flexibility than the contact member whereby firm and even pressure is applied through the said fulcrum to maintain the coacting contacting portions in continuous and smooth engagement; and more particularly the pressure applied to the contacting -ortion through said fulcrum is at a point ra ially chest with 1929. Serial No. 845,174.

respect to the point of hearing contact pressure.

M invention further resides in a. paratus of the character hereinafter descn ed and claimed.

For an illustration of some or the forms my invention may take, reference is had to the accompanying drawing in which:

Fig. 1 is a side view, partly in section, or a variable contact device.

Fig. 2 is an elevational'view of the device illustrated in Fig. 1.

Fig. 3 is a detailed'lower plan view of contact structure.

Fig. 4 is a detailed uppen lan view of the contact structure shown in ig. 3.

Fig. 5 is a side view of the structure illustrated in Figs. 3 and 4.

Fig. '6 is a detailed view of modified contact structure prior to assembly.

Fig. Z is an endwise view of contact structure looking towards the free end thereof.

Fig. 8 is a partial View illustrating the contact structure of Figs. 3 and 4 in engagement with a resistance element.

- Fig. 9 is a lower plan View of another modilied form oil contact structure.

Fig. 16 is a side view of the structure shown in Fig. 9.

Fig. ii is a diagrammatical illustra radio receiving circuits.

"Referring to, Figs. 1 and 2, a casing molded insulating material of suitable characteristics comprises a cup-like member having rotatably and centrally mounted in a wall thereof the shaft 5. An operatin knob d'l is secured to one end oi shalt J an a boss or hub H is secured to the other end thereof as by a set screw Hi. or equivalent. A pair of resilient superimposed leaf members A and S comprising rotatable contact structure are secured to hub l-ll by an upset portion Q in a manner presently described. The resilient leaf member 8 engages the upper face or? e resistance R and is in turn engaged tion of till ill)

by an abutment or fulcrum P carried by the I other leaf member A. The resistance element or resistor R comprises a resistance wire wound in any suitable manner u on a curved insulating strip 0 secu'ed to t e casing M atits o posite ends by the bindin posts or screws 1 and O2. Hub H, to whic the contact arm S is electrically connected, is frictionally engaged by a resilient positioning and conductin memberW throu h which shaft J exten s, and whic is apted to maintain shaft J in operative position wherein the knob J1 serves as a stop member, and also to provide electrical contact between arm S and a binding post 03 which secures member W to the casing. v

' Referring more particularly to Fi 3 to 5 inclusive, hub H comprises an annufil r portion Q over which the leaf spring-like members S and A are placed in superimposed position, after which portion Q is upset to clamplor rivet the sprin members firmly to hub The lower lea member" S, Fig. 3,

com rises atapering. portion having a plane or at contacting portion or. shoe K at its outer end and is notched or otherwise reduced in width ad'acent its free end-to form a com-- .paratiyely t inneck portion N which is less resistant to torsional stress than other portions of the memberl In other words, contact shoe K is freely about its ongitudinal axis in response to comparatively small torsional moments. Members is furthermore preferably slotted atSl thereby insuring comparative lightness and exibility of the contact arm.

7 As will be noted in Fig. 4, the upper or overlying member A, being slotted only at {L1, is less flexible than contact arm S. Adacent the outer or free end of member A are abutments P and P disposed substantiall along the longitudinal axis of A and extend ing towards the upper surface of contact shoe K. The resilient leaf members A and S normally tend to assume the curvilinear shapes illustrated in Fig. 5.

In Fig. 6 thereis illustrated a leaf member A having a single abutment P at its free end I such as is shown in Fig. 1. The leaf members A and S are furthermore shown prior to assembly with respect to hub H, and upon which they may be firmly united by the riveting portion Q.

The contact structure previously described is particularly adapted to engage,'asby a sliding action, the surface of a resistanceelement, particularly of the type comprising a coiled resistance wire whose edge or contacting surface is apt to have slight or minor irregularities, but which nevertheless are s'ufiicient to seriousl interfere with smooth and even mechanica operation of an ordinary contacting arm therewith. In other words, an ordinary contact arm riding upon such a surf often produces a scraping noise, particularly when rm-itted to oscillate rather' the contact arm and resistance are comprised within radio receivm circuits, as in the volume control circuit, us to the fact that the edges of the contact do not ride evenly over.

the irregularities of the resistance element.

Furthermore, the area of contact, and there-- fore the contact pressure, is apt to vary widely resistance R. The contact arm S, it will be noted, is flexed in such manner that contact .shoe K is in substantially a horizontal plane by reason of the engaging abutments P and P1 on the less resilient leaf member A. Accordingly, it will be observed that in addition to the ressure exerted upon the contact shoe K by t e resilient arm S there will be uneven greater and more positive pressure exerted by the superimposed member A through the abutments P and Pl. If the contact arm S were solely relied upon to provide proper contacting pressure, the comparative lightnessand flexibilit of this member would cause contact shoe ii to contact unevenly and unsteadily with the resistance R. If on the other hand a contact. arm having the characteristics of member A were solely relied upon to maintain propericontacting engagement with the resistanceeilement, the edges of the member, due tothe greater bearing pressure exerted bythe more ri 'd arm, would tend to dig in or catch along e. irregularities of the resistance element, and so result in noisy and unsatisfactory operation.

By providing a comparatively flexible and resilient contact arm and a more rigid or supporting arm therefor, about whose longitudinal axis the contact arm may'oscillate, sufiicient bearing pressure is maintained at the contacting surfaces while at the same time reducing or practically eliminating the dragging action of the contact portion, and the consequent increased friction and scraping sound due thereto. To this end, the abutment or abutments engaging contact shoe K are disposed substantiall along the longitudinal axis of arm S, t ereby acting as a fulcrum or pivot point about which contact shoe K ma oscillate or rock about its lo tudinal axis to conform to the irregularities of the resistance element. Such oscillatory movement, ermittin'g the plane of the contacting portlon to coincide or engage in multioint contact with its coacting'surface, is

urthermore facilitated by the comparatively v flexible necked-in portion N of the; contact arm whereby the torsional moment required e contact shoe may be compare-- tivel small. Accordingly, as shaft J 18 reta the contact shoe Kwillride evenly over neck N.

moaooo the resistance element R, rocking with respect to its longitudinal axis about the abutment or abutments at the end of member A as the surface of the resistance element vgries in contour.

l he radial position of the abutment P is preferably beyond the bearing contact surace and enga es the extreme outer end 0 contact shoe to maintain it in firm and continuous contact with the resistance element. Or the abutment I may be directly above the bearing contact surface, depending on the curvature of the movable contact member. Accordingly there isa tendency for the movable contact shoe to ride tangentially along the top or the top-outer ed of the resistor, thereby obviatin any igging in action of the edges of t e movable contact. If abutment P were disposed on the opposite side of.the point of contact, other factors being the same, contact shoe K would tend to tilt inwardly and away from its normal plane because of the relative weakness of This would be an undesirable fea-. ture since it is essential for smooth and quiet operation that the plane of the contacting portion be substantially parallel or coincide with the plane defined by the circular contact edge of the resistor. In other words, the contact shoe should not ride along the to inner edge of the resistor for there wou d then be a tendency for the edges of the shoe to dig in and produce a scratching sound. The above described feature is clearl illustrated in both Figs. 1 and 8, the ad itional abutment P1, Fig. 8, being provided to allow for irregularities in the curvature of the re sistance element with respect to the axis at J. The abutment, instead of the individual depressed portions P and P1, ma evidently comprise a continuous ridge or -punching' I in the supporting leaf A, the ridge extendtill ing substantially co-incident with the lon= gitudinal axis of contact arm S, and for such length as is required by the variation in radius of curvature of the resistance element. Ac"

cordingl the abutment or member A. serves not only to properly position the longitudinal axis oi thecontact shoe K, but to act as a fill crum or pivot about which the contact shoe may oscillate or rock to maintain even multi point contact with the resistor.

Figs. 9 and 10 illustrate a further modification of my contact arm wherein but a single lest member is employed. Boss H has riveted thereto at Q in the manner described above a tapering resilient member A from which tongue lihe portion is stamped at I. stamped out portion, bent in reversed direction at its narrowest portion U, comprises a contact shoe Kl carried by a compars-tively narrow flexible strip Ni secured at U to leaf member A. As in the previous instances, the contact shoe K1 is carried by a comparatively flexible or resilient member having small resistance to torsional stress, and is adapted to be urged when in o rative position, firmly into engaement wit its coafitin surfhaoe immedia dy underrpeath the soe yte more 1'1- su ing arm through the abutment W'B ii assembled in the manner illustrated in Fi 1., the abutf ment P extends radially beyon the bearing to maintain the contact surface and serves plane of contact shoe K1 substantially parallel to'the plane of the coacting contact edge of the resistor. As in the previous instances, the abutment or fulcrum P is disposed on the longitudinal axis of both member A. and the contacting shoe K1 thereby permitting oscillatory movement oi the contacting portion in the manner above described. I

In Fig. 11 there is diag trated a portion of radio receivin circuits in which the above described variab e contact device may be employed to effect volume control. A shielding conductor 1 is suitably connected to round E. An antenna lead 3, disposed within the shielding conductor is connected at one end to the antenna 6, and at the other end to a terminal of the resistance element R comprising volume control apparatus. A. movable contact K coasting with the resistance element is electrically connected to the shielding conductor 1 and .an artificial or set ground E, The (ipposite terminals of resistance element are connected by conductors 2 and 5, which are twisted with respect to each other, in the manner illustrated in a copending application Serial No. 299,933, filed August 16, 1928, by. Prayer, to an input coupling element L. Associated therewith is an electric valve V of the thermionic type having a grid 9 to which the coupling element is connected, a filament heated by alternating current derived by means of transformer 7 from a suitable source at supply and a plate p connected in the output circuit oi the valve comprising the primary of the step-up transformer T, whose secondary isassociated in the usual manner with a tuning condenser G.

As the movable contact K is adiusted with respect to resistance R, appreciahle variation in the contact pressure due to uneven or rough contaotin engagement may produce a microphonic e ect, which when amplified in the circuits of the radio receiving apparatus, pro duces obiectionable noises similar to those produced by static in the sound reproducer. i have found that when my variable contact device is utilized in the volume control cirsuit, the action oi.- contact K is practically noiseless due to the tact-that even bearing pressure between the enacting elements is substantiall maintained at alltimes. lilo apreciable' microphonic client is therefore pro= need, and the tone qualities of the radio receiving apparatus are not marred during adjustment of the volume control.

rammatically illus- While the sppsi'atus herein illustrated coni stitutes a preferred form of my invention, it shall be understood that a reesonehie del pcrture in construction may be made without departing from the spirit of my inven tion,

What I claim is:

1, In e volume control rheostn-t ion i'edio.

. receiving sppsretus heving e helix oi resistmediate said silient contect member, said reduced section end said abutment permitting cooking of said contact shoe to ensure smoothly continuous variation of resistance during movement g of ssid srm and to meintain direct wiping e ment, means for shoe, seid contact rock contact between a, plurality of turns of seid helix and said contact shoe.

2., In a volume controlrheostet for redio receiving apparatus having e resistance elepreventing noise-producing imperfect contact theveet comprising e contact member having e shoe for engaging said element simultaneously et at plumlity of points along the psth of movement oiseid member having e-reduced section between seid shoe and the support oi soid contact member less resistant to torsionel sti'essthen said shoe, end a member seidshoe into enge, ement with said resistonce element throng e fulcrum ermitting ing of said contact shoe fecilituted by said reduced section to meintein multi-point direct wiping contact between said resistance element and said shoe.

3. In a volume control rheostet for radio receiving apparatus having a helix of resistance wire, means for preventin noise-producing imperfect contact with sei helix comprising a, contact member having a shoe. for on aging said helix simultaneously at, a. plurality of turns thereof, and a reduced sectlon intermediate said shoe end the support of said contact member, and s resilient arm overlying said contact member and engaging said shoe through an abutment forming a fulcrum per mitting rocking of said contact shoe to maintain direct wiping contact between said helix and said contact shoe. 4. In a volume control rheostat for radio receiving apparatus having a resistance element, means for preventing noise-producing imperfect contact thereat comprising a resilient contact member rotatably supported at one end thereof, and having a contacting portion at its free end for engaging said resistand it reshoe and e support for ssid E8-- pi essingc ance element simultaneously at a plurality'of path of movement of said points along the H contacting ortion to effect a direct wlpmg contact with said resistance element, and a member mounted coaxislly'with end in superposed i'eletion to said contacting portion having s fulcrum enga in suid contecting poition st e point re iel with seid resistance element.

EDMUND G. LQDGE.

7 beyond its contact 

